Paul Yaw wrote:

Archie,

The rotary is quite insensitive to imbalance.  I feel they should be
balanced anyway.  It is not uncommon to see an engine with one rotor 30
grams heavier than another.  The big question is how much oil is in the
rotor.  Since I have never gotten an accurate answer, I cc. each and
every one.  Mount the heavy rotor on a rotary table, and remove material
equally around the perimeter, and on both sides to make the rotors equal
in weight.  Once this is done, spin the rotors individually and
rebalance if necessary.   To make up the bob weights, add the weight of
the rotor, all seals and springs, AND the oil.  After that you just spin
it and balance it straight up. Since we can never really know exactly
how much oil is in the rotor, In my opinion, it will never be perfectly
balanced.  The upside is that it doesn't seem to matter a great deal.
If you build a single rotor, get ready to add a LOT of heavy metal to
the counterbalances.

Paul Yaw

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